Holling’s adaptive renewal cycle [1, 2] continues the kind of thinking behind the logistics equation in population ecology, except instead of applying it to populations, Holling’s model takes the ecological community as its focus. One good example of an ecological community is a forest. Prior to a forest existing, some kind of natural force (flood, fire, infestation etc.) clears the ground. On that freshly exposed resource, a r-selection regimes (P) takes root, followed by K-selection regimes (A) as the carrying capacity of the resource is reached.

With the intensification of the K-selection regime, organisms get larger and more internally differentiated, but that is not all that happens. Organisms specialize and differentiate from each other as well. The forest evolves into a community of organisms connected together in complex food webs. As niches get filled, the community continues to mature, and even more specialized organisms fill the new “niches between the niches”, making use of any exposed material and energy resources they can evolve to exploit. The overall connectivity of the system increases.

Eventually the forest becomes what ecologists call a “climax community” – a fairly stable, densely interconnected system of living organisms. In PAEI terms, we can say that as organisms developed more internal differentiation (A), they also developed more external interdependencies (I). This process of both internal and external differentiation and integration eventually binds up most of the free matter and energy in the ecological community. The community itself then becomes the “big apple” – the big source of matter and energy that could be consumed by other organisms if it was released. Resources bound up within the climax community can be released, as mentioned before, with an act of “creative destruction” – flood, fire, infestation, drought, migration, fluctuation or any other such disruption (E). That creates new opportunities, and the cycle starts all over again.

In Holling’s adaptive cycle, we see P, A and I patterns of activity. Forests are fairly passive systems for the most part, so we don’t see the forest as a whole out foraging for new opportunities. Instead, for E we see the kinds of large-scale, disruptive, discontinuous changes that E concerns itself with.
So not all concerns are represented in the same way in the adaptive renewal cycle, even though all four concerns are represented.

To recap: starting with an exploitation-heavy race for resources/energy reduction opportunities, the cycle shifts into a phase of consolidation and stability, followed by disturbances/perturbations with a
resulting reorganization. The four stages: exploitation, conservation, release and reorganization, are illustrated below (based on Berkes et al.[3]), with PAEI labels attached in the relevant places.

This is a two-dimensional image. The cycle may be better visualized in three dimensions as a wavy ring. If the third dimension was represented in the above image, it would add the dimension of resilience to potential and connectedness, to complete Holling’s model (Allison & Hobbs, [4]). Communities are resilient from the release phase through reorganization and into exploitation, but the increasing connectedness and interdependency that shifts exploitation to conservation prior to release makes the system more brittle. A delicate balance is struck that must be maintained or else the web may come apart and the release phase will commence.

This model gives us a good picture of how a PAEI (actually PAIE, in this case) sequence can emerge in the lifecycle of a natural system. It also illustrates levels of concern in the natural world corresponding to PAE and I.